1. Field of the Invention
The present invention relates to a backlight unit which feeds power to a cold-cathode tube, and more particularly to a backlight unit which feeds power to a plurality of cold-cathode tubes connected in series from a single inverter circuit transformer, and further relates to a liquid crystal television which employs the backlight unit.
2. Description of Related Art
Generally, the backlight unit for driving the backlight which illuminates the liquid crystal display from the back side has been well known. The backlight unit feeds AC power generated by the separately-excited or self-excited inverter circuit transformer to the backlight so as to be illuminated.
Japanese Unexamined Patent Application Publication No. 2005-5059 discloses the backlight unit which employs at least two cold-cathode tubes as the backlight, each of which receives power from the single inverter circuit transformer.
Japanese Unexamined Patent Application Publication No. 2005-190835 discloses that the single self-excited inverter circuit transformer feeds power to two cold-cathode tubes connected in series.
In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2005-5059, the number of the inverter circuit transformers has to be increased in accordance with the number of the cold-cathode tubes, which results in the cost increase.
In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2005-190835, variation in the tube current fed to the cold-cathode tube may result in uneven luminance. Even if the constant electromotive force is applied to the secondary coil of the inverter circuit transformer, the variation in the value of the tube current applied through the cold-cathode tube may make the light emitting luminance uneven. As shown in FIG. 5A, two cold-cathode tubes RL1 and RL2 are vertically arranged. When the tube current is applied from the RL1 to RL2, the lower portion of the backlight 1 has the higher luminance than that of the upper portion as shown in FIG. 5B, causing the luminance gradient. This may result in the uneven luminance of the liquid crystal display, and accordingly, the viewer may feel uncomfortable with the view of the display.